1. Field of the Invention
The present invention generally relates to image sensing systems and more particularly relates to an image sensing module using a lensless optical system to produce digital images.
2. Description of the Related Art
It is not uncommon to see a whiteboard in every meeting room of a corporate in America. The whiteboard provides an informal medium for meeting attendees to communicate effectively and interactively. Like a scratch paper but more presentable, a whiteboard allows a speaker to use colorful markers to write, erase, draw, and modify what is being discussed and agreed upon among meeting attendees.
Whiteboards offer several advantages over chalkboards including a clean white surface which provides for greater contrast over the traditional green background of chalkboards. In addition, writing on a whiteboard is easier for many than on the traditional chalkboard. For example, the smooth writing surface of the whiteboard allows easy use of the erasable felt tip markers used on whiteboards, whereas the chalkboard surface provides a somewhat scratchy surface to hold the chalk used for writing on such surfaces. In addition, many users prefer a whiteboard to a chalkboard simply because the marker may be gripped easier than the chalk and does not mark the user's hand when gripped.
Recently, whiteboards have been developed to allow the user writings and notations entered upon the whiteboard to be printed or stored to a digital computer for storage, display and manipulation. A whiteboard, called Plus Boardfax, from Plus Corporation is designed to provide the capabilities to capture the information presented in the whiteboard. FIG. 1 illustrates an exemplary whiteboard 100. It includes a frame 102 and a rotatable canvas or writing surface (sheet) 104 for writing. When a page of writing is done, sheet 104 is caused to rotate towards an image scanning module 106 that is typically concealed in frame 102. As sheet 104 moves across image scanning module 106, marks or anything in writing are scanned by image scanning module 106 that subsequently generates an image thereof. The image can be then printed on a sheet of paper 108 by a concealed thermal printer for distribution or permanent record.
The basic principles of whiteboard 100 are the use of an image scanning module or system that comprises an image sensor, an optical lens and an illumination system. The image sensor comprises an array of photodetectors responsive to reflected light focused by the lens and from writing sheet 102. Each of the photodetectors produces an electronic signal representing the intensity of the reflected light. The electronic signals from all the photodetectors are then readout for printout or processing.
It can be perceived that the cost of the image scanning system goes up dramatically as the size of scanning width (i.e. the height of sheet 102) increases, so as the whiteboard 100. One of the factors in the cost is the complicated design of the optical system that must linearly focus light from sheet 102 onto the image sensor in the image scanning system. To reduce the cost of designing such optical system, multiple image scanning modules are sometimes used, namely each of the image scanning modules is responsible for a predefined area of sheet 102, signals from all the image scanning modules are then stitched together to form a complete signal for subsequent processing and output. Nevertheless, the use of multiple image scanning modules introduces a complicated process of aligning all the multiple image scanning modules, namely image scanning modules must be aligned precisely to avoid overlapping between two adjacent image scanning modules so as to alleviate data analysis and processing due to the overlapping. There is, therefore, a desire to have a cost-effective optical system in an image scanning system so that there would be no need for multiple image scanning modules.
One of the benefits and advantages of the whiteboard over the traditional chalkboard is the use of powderless markers, and the whiteboard has begun to appear in education facilities and even in many families for children's educational activities. Further the whiteboard can potentially be used for discussion between two people and generates images to be reviewed by a third party in a remote site through the Internet. With the increased applications and popularity of the whiteboard, there is indeed a great demand for a low-cost image scanning system that can be used in applications like the whiteboard.